1. Field of the Invention
The present invention relates to a video signal processing method for searching corresponding points of stereo video pair and apparatus for processing.
2. Description of Prior Arts
Recently, in appreciating stereo video, technology utilizing parallax of both eyes to watch stereo video on video display is well known. Stereo video pair means a pair of video pictures taken from each eye position of left and right. When we watch stereo video pair with each eye for corresponding each video picture of the stereo video pair, we perceive the subject three dimensionally, uniting the two video pictures of stereo video pair. In addition, the video signal processing method for searching corresponding points of stereo video pair and processor is known. When an optional pixel in one side video picture composing stereo video pair is defined as a fixed pixel, the corresponding point means the pixel corresponding to the fixed pixel in the other side video picture. That is the pixel which corresponds to the same point of the same subject in the same video picture. We can get three dimensional information by calculating the difference between coordinates, regarding each pair of corresponding pixels in stereo video pair. This can be applied to the three dimensional measurement of the subject.
Same size comparing area(called "window" hereinafter) are set in both pictures of stereo video pair. Corresponding pixels are searched by comparing the similarity of the both windows. To compare similarity, there is a method to get sum of squared difference between each corresponding pixel value in both windows. This is called SSD(Sum of Squared Difference) method. When the sum of squared difference is minimum under the condition that the window of one side is fixed and the one of the other side is moved up and down and left and right in video, it is judged that the pixels in both windows are most similar.
Method for searching corresponding points, using SSD(Sum of Squared Difference) is proposed in thesis, for an example, "Stereo Matching using Plural Standard Lines" on p1317.about.1327 in the Transactions of the Institute of Electronics, Information and Communication Engineers DII Vol.J75-D-II August 1992. This is the method to get, using different standard lines in stereo video pair, all sum of each corresponding point pair distance inverse square sum SSD. With this method high accurate search for corresponding points is possible.
The above mentioned technology has the following problems to improve.
When searching corresponding points in comparing SSD of windows, in case that the pixel values in the windows are not varied and the density difference is small, if the window size is small, it sometimes happens that similar windows increase and the probability of false corresponding becomes large. On the other hands, when the size of windows is smaller, the more accurate is the comparison result of SSD on the edge part of the subject of which density difference is large. Namely, when the window is enlarged, searching accuracy becomes worse, because the pixel value difference in other part effects on SSD considerably.
However, with usual method for searching corresponding points in stereo video pair, satisfactory accuracy cannot be obtained, because a fixed window sizes are used.